Minerals which display moderate to strong birefringence may display a change in relief as the stage is rotated, in plane light.
This change in relief results from the two rays which exit the mineral having widely differing refractive indices - examine in Lab 2.
With the upper polar removed, many coloured anisotropic minerals display a change in colour - this is pleochroism or diachroism.
Produced because the two rays of light are absorbed differently as they pass through the coloured mineral and therefore the mineral displays different colours. Pleochroism is not related to the interference colours.